Colorado bird flu cases show how extreme heat may be complicating efforts to control the virus

The CDC says the threat to the general public from bird flu remains low.Photo byGetty Images

Intense heat could have contributed to the sickness of five employees who became ill last week while removing a big group of chickens infected with the H5N1 virus from Colorado, health authorities reported on Tuesday.

“At the time transmission is thought to have occurred, Colorado was experiencing 104-plus-degree heat,” and it was probably hotter inside the barns, said Dr. Nirav Shah, principal deputy director of the US Centers for Disease Control and Prevention. The CDC and the Colorado Department of Public Health and Environment are investigating the outbreak. This made the use of personal protective equipment a challenge, Shah said.

Moreover, massive industrial fans were in operation to cool the overheated barns, circulating air, dust, and feathers. It's known that feathers from sick birds can carry the H5N1 virus.

"We recognize that those big fans were circulating a lot of air, making it challenging for the workers to keep a proper seal or a secure fit with their masks or eye protection," Shah explained.

So far, the CDC has confirmed four cases in Colorado. Another case was identified at a state lab and is currently being verified at the CDC. This situation has rapidly increased the number of farm workers infected with the H5N1 virus in the US, marking the largest number of infections linked to a single farm.

In 2022, a person employed in poultry in Colorado was found to have H5N1. Additionally, four other individuals working on farms have also been diagnosed with the virus, with one case in Texas, two in Michigan, and another in Colorado. It's suspected that the actual number of cases might be lower since farm laborers often hesitate to undergo testing due to concerns about potentially losing their jobs and earnings.

Analyzing the genetic makeup of the virus from a recent human case involved in the culling of poultry was comforting for Shah, as it did not reveal any changes that could suggest the virus is becoming more contagious to humans. The tests also indicated that the virus was closely linked to the strain affecting cattle.

Following a request from the state of Colorado, the CDC dispatched a 10-member team to aid in the investigation and tracing of contacts in the outbreak. A total of 60 individuals have exhibited symptoms indicative of avian influenza, with all but five testing negative at a state facility, Shah reported.

"We've observed a significant increase in testing at this specific farm in Colorado," he noted.

All workers remained healthy, and several experienced common flu symptoms such as conjunctivitis or eye infections, fever, chills, coughing, and sore throats. The employees have received antiviral drugs and are on the path to recovery.

In total, around 160 individuals are participating in the culling, or extermination, of 1.8 million chickens that lay eggs on the farm in Colorado. This farm is a major producer of eggs, though the authorities have not disclosed its name. The extermination process is set to go on for an additional 10 to 14 days.

The exact cause of the bird's infection is unknown, but the viruses found in the birds are very similar to those affecting dairy cows, according to Dr. Eric Deeble, who serves as the acting senior adviser for the H5N1 response at the US Department of Agriculture.

The Centers for Disease Control and Prevention (CDC) believes that the risk to the general public from the H5N1 bird flu virus is minimal.

Nonetheless, the workers on the farm face a greater risk of contracting the disease, which has been spreading from both domestic and wild birds to dairy cows and other animals.

For safety, the CDC advises individuals handling sick or deceased animals, such as cattle or birds, to don personal protective gear, or PPE, which encompasses waterproof overalls, a face mask, goggles or a face shield, footwear, gloves, and a headpiece.

Employees tasked with the slaughter of chickens in Colorado were mandated to wear the complete set of gear, yet the harsh weather conditions made it challenging to maintain. "We recognize that the use of PPE, especially masks and eye protection, was suboptimal," Shah mentioned.

The United Farm Workers labor union has raised doubts about the practicality of the CDC's guidelines, especially amid an unprecedented heatwave across much of the United States this summer. It has urged the CDC to revise its PPE advice to allow for wider compliance.

"These individuals are risking their lives for a virus that remains largely mysterious, with no viable means of protection against either the virus or heat-related illnesses," Elizabeth Strater, the director of strategic campaigns for United Farm Workers, stated on Tuesday. "They are placed in an untenable situation."

Workers wear fluid-proof coveralls, Strater points out, which prevent sweat from cooling their bodies, making it easy to overheat. In dirty, wet environments like a barn, masks, and respirators can become clogged or soggy within minutes.

The CDC is working to update its guidance on personal protective equipment (PPE) to better handle the heat. "We've included a specialist in this area, an industrial hygienist, in our team, to help implement better engineering solutions that could make wearing PPE more consistent and more comfortable," Shah mentioned.

Shah also noted that it's time for the CDC to consider vaccinating agricultural workers, following Finland's example, to provide an additional layer of defense against the virus and the risk of another pandemic if it spreads.

"They should be prioritized not just for the ethical reason of protecting their lives through vaccination, but also because they represent a relatively small group in comparison to the protective barrier they could create for the general public," she explained. "This isn't an overwhelming number of people to protect. These individuals are at the forefront and are highly exposed."

While US health officials have indicated they have no immediate plans to distribute an H5N1 vaccine, they are preparing several candidates for distribution in the event the virus becomes more severe.

In May, the US Department of Health and Human Services placed an order for 4.8 million doses of H5N1 vaccine from bulk ingredients in the country's Strategic National Stockpile. These doses are anticipated to be available by the month's end.

By early July, the HHS had agreed to pay Moderna $176 million to aid in the development of an mRNA-based vaccine against H5N1. The agency expects to receive the results of the phase 1 clinical trial on the vaccine's safety by the end of the year.